1. Field of the Invention
This invention relates to the construction of air cooled hysteresis brake assemblies.
2. Prior Art
It is a well known phenomenon that a permeable disc rotating in a magnetic field will have eddy currents induced on the rotating disc and that such eddy currents will produce a magnetic field which opposes the first magnetic field thereby producing a force which tends to damp the rotation of the disc. The magnitude of the force is proportional to the strength of the magnetic field in which the permeable material rotates. The application of this force results in the generation of heat within the rotating disc. If enough heat is generated the rotating disc must be cooled to avoid damage.
In the commercial construction of such eddy current (or hysteresis) type brakes, it is desirable to obtain as much braking force as possible and yet at the same time keep the size of the brake assembly relatively small. In order to obtain maximum braking force, prior art brakes were constructed in the shape of a cup. (See U.S. Pat. No. 3,700,941 to Duncan). Such brakes had a disc like portion located perpendicular to the axis of rotation and a wall section extending axially to one side of the disc portion. A first pole member would be located radially outside of the wall and a second pole member would be located radially inside of the wall. In this way the eddy currents and resulting braking force would be produced in the wall member, substantially at a radial distance equal to the radius of the disc member. This would maximize the lever arm of the braking force and thus produce maximum braking torque. A major disadvantage with this type of construction has been that the resulting structure is longer than desired in the axial dimension and the brake assembly must be lengthened to accomodate the axial dimension of the walls of the brake member.
In an effort to construct a brake assembly of compact dimensions, various attempts have been made to design and employ a brake member which is a simple disc, extending perpendicular to the axis of rotation, having no wall component extending in the axial direction. If such a brake assembly were feasible, it would result in a compact brake, whose axial dimension was less than prior art designs employing a cup-like brake member. Prior attempts to employ a disc-shaped brake member have proven unsuccessful for a variety of reasons. Primary among the reasons for these unsuccessful attempts has been the inability of such designs to adequately remove heat from the rotating disc. To prevent deformation of the brake disc, the heat must be removed uniformly on both sides of the brake disc.
It is desirable to use a brake member which is disc shaped so as to reduce construction costs and simplify the manufacturing process. However, a disc shaped brake member having the same radius as a cup shaped brake member will produce less braking torque than the cup member for a given strength magnetic field. Thus, to increase the braking torque output of the disc shaped braking member, the strength of the magnetic field must be increased. This produces greater heating of the disc member than would be produced in a cup member producing the same braking torque.
Prior hysteresis brake designs employing a disc shaped brake member were unsuccessful in part because they could not overcome the increased heating problems.
It is therefore an object of the present invention to provide an eddy current hysteresis type brake assembly which employs a flat disc shaped brake member.
It is a further object to provide an eddy current hysteresis type brake assembly which employes a flat disc shaped brake member and also developes a braking torque equal to or greater than the torque developed by a comparably sized brake assembly employing a cup shaped brake member.
It is another object to provide a brake member which is simple to manufacture and lower in cost to manufacture than brake members of the prior art. It is yet a further object to provide such a brake assembly which because of efficient and novel cooling means does not suffer adversely due to the heat generated in the brake member.
It is an object of the present invention to provide an eddy current hysteresis type brake assembly which employs a flat disc shaped brake member which therefore results in a compact brake assembly structure and requires a reduced amount of materials for its construction.
It is still another object to provide such a brake assembly which cools both sides of the flat disc shaped brake member equally and uniformly thereby resulting in increased smoothness of operation, minimum warpage and wear and maximum brake life.
It is an object of the present invention to provide a compact eddy current hysteresis type brake assembly which can generate higher braking torques than similar brake assemblies of prior art designs and larger size.